Radomes are structures that are used to protect antennas (e.g., radar antennas) and associated equipment from environmental exposure. Thus, radomes may be subject to both physical and electromagnetic requirements and specifications. For example, radomes are often used in various types of aircraft and missiles carrying radar equipment, and such radomes must be aerodynamic and capable of withstanding physical and thermal stresses encountered during flight. Radomes also are typically subject to electromagnetic performance requirements and specifications such as, for example, minimum transmission loss, minimum reflected power, minimum beam deflection, and minimum pattern distortion. There is often a trade-off in the design of a radome between physical performance requirements and electromagnetic performance requirements.
The term “radome” was derived from the terms “radar” and “dome,” although, as used herein, the term “radome” means and includes any structure configured to protect an antenna from environmental exposure and through which electromagnetic radiation is transmitted to or from the antenna. Radomes may have any shape or configuration, and are not limited to dome-shaped structures, and may be configured to transmit any range of frequencies of electromagnetic radiation therethrough.
There are many different materials used in constructing radomes and many different cross-sectional radome configurations including single layer (often referred to in the art as “monolithic” or “solid-wall” configurations) and multi-layer or “sandwich” configurations including, for example, what are known in the art as “A-sandwich” radome configurations, “B-sandwich” radome configurations, and “C-sandwich” radome configurations. Such radome configurations are discussed in, for example, A. W. Rudge, K. Milne, A. D. Olver, and P. Knight, eds., THE HANDBOOK OF ANTENNA DESIGN, Vol. 2, Chapter 14, Peter Peregrinus Ltd., London, and M. I. Skolnik, INTRODUCTION TO RADAR SYSTEMS, Chapter 7, McGraw-Hill, New York, N.Y.
The “A-sandwich” radome configuration includes a relatively thick inner core that is sandwiched between two relatively thin outer “skin” layers. The inner core is formed of a material that exhibits a low dielectric constant (e.g., a foam material, or a honeycomb structure), and the outer skin layers are formed of a material that exhibits a relatively high dielectric constant. The dielectric constant of the core may be less than the square root of the dielectric constant of the skin layers. The dielectric constant of the core may be reduced by reducing the density of the core material (e.g., by increasing porosity in the core material).
The “B-sandwich” radome configuration includes a relatively thin inner core that is sandwiched between two relatively thick outer skin layers. The inner core is formed of a material that exhibits a relatively high dielectric constant, and the outer skin layers are formed of a material that exhibits a relatively low dielectric constant. The dielectric constant of the core may be greater than the square of the dielectric constant of the skin layers. B-sandwich radomes may exhibit higher power transmission efficiencies relative to A-sandwich radomes, but the physical properties exhibited by the materials of the outer skin layers in B-sandwich configurations may not withstand the conditions experienced in high-temperature, high-velocity applications such as those encountered by radomes on missiles.
What is referred to in the art as a “C-sandwich” radome configuration consists of two contiguous A-sandwiches. In other words, a C-sandwich radome includes two “core” layers that exhibit a relatively low dielectric constant that are separated from one another by a central skin layer. An outer skin layer is also disposed on the outer surface of each core layer, and the exposed major surfaces of these outer skin layers provide the interior and exterior surfaces of the radome. Sensitivity to frequency, incident angle, and polarization may be reduced in the C-sandwich radome configuration relative to the A-sandwich and B-sandwich radome configurations.
Radomes that are lightweight, physically strong, tough, and wear-resistant, and that exhibit desirable electromagnetic performance characteristics continue to be sought for use on aircraft and spacecraft.